Recent studies in fishes have suggested that the terminal nerve (TN) rather than or in addition to the olfactory system mediates certain pheromonal influences on sex responses. Experiments are proposed to examine possible TN control of two sexual responses in male goldfish. Attempts will be made to correlate deficits in sperm release (SR) in response to olfactory tract stimulation and sexual arousal (SA) in response to female pheromones with the relative extent of experimentally induced damage to the TN as opposed to the olfactory system. Horseradish peroxidase (HRP) tracing methods will be used to verify the presence of TN cells and fibers. TN fibers also run in the optic nerve (ON) in goldfish and electrical stimulation of this nerve can evoke SR. Experiments will test the hypothesis that the SR results from antidromic activation of the TN fibers. TN and retinofugal components of the ON will be independently eliminated using surgical procedures and the ON stimulated to test its ability to mediate SR. In addition, the ON will be stimulated in free-swimming fish as a first step in determining whether or not antidromic activation of the TN fibers can also elicit sexual arousal. The results of the proposed research should provide evidence for or against TN mediation of reproductive responses. Close similarities in the anatomy and biochemistry (LHRH immunoreactivity) of the TN in species ranging from goldfish to man suggest that the findings would relate to the sensorimotor control of vertebrate sexual behavior in general. They could also be instrumental in defining the function of new sensory mechanism. With regard to possible clinical relevance, LHRH, the likely transmitter or modulator released at TN endings, has been reported to be effective as a drug treatment for certain human sex-behavior problems. It is quite possible that some of the drug effects are related to normal TN functions.